American officials have become so frustrated with a Mexican drug lord's ability to elude capture that they've started telling jokes about it.

Time and again, the U.S. provides Mexican law enforcement with precise intelligence about the safe houses where Joaquin "El Chapo" Guzman, head of the Sinaloa drug cartel, is hiding. And every time the Mexicans raid a house, the man that the U.S. government calls "the most powerful drug trafficker in the world" manages to escape at the last minute through the back door.

Behind the jokes, however, is concern that someone in Mexican law enforcement is tipping off Guzman, allowing him to escape just ahead of the raids. During the 1990s, problems with leaks of U.S. intelligence helped delay the capture or killing of several top players in the Colombian drug cartels.

In El Chapo's latest escape, he apparently went out the back door of a mansion in the beach resort of Los Cabos just before Mexican Federal Police raided the house. Several of his alleged associates were arrested and are in custody. The raid in late February came just a day after Secretary of State Hillary Clinton and other foreign dignitaries were in town for a meeting, and the U.S. was able to provide Mexican officials with precise intelligence about Guzman's whereabouts.

In another recent near miss, according to U.S. officials, the Mexicans came so close to catching Guzman that his coffee was still warm.

U.S. intelligence about Guzman's whereabouts is typically pinpoint, say officials. The U.S. might, for example, be able to find the city block where the kingpin is staying, and then narrow his location down to two or three houses.

The U.S. holds the information closely until Guzman's exact address is known. The U.S. then shares the information with only a few key people in the Mexican federal police and the military who have been reliable allies in the drug war. Each time the Mexicans mount a raid, however, El Chapo escapes.

One possibility, say officials, is that after receiving the intelligence the Mexicans are simply slow off the mark, giving Guzman time to flee before the raiding party arrives. After so many close calls, however, there has been unavoidable speculation about another possibility, that there is leak somewhere in the chain, and someone is warning Guzman. Despite the concerns, efforts to catch Guzman, and the sharing of intelligence, continue.